If a power supply to an audio amplifier is switched on when a loudspeaker or a headset is already connected to the audio amplifier, a click may be heard due to transient signals occurring as quiescent DC voltages and currents are established in the amplifier. Similarly, a click may be heard when the power supply is switched off, due to transient signals as the quiescent DC voltages and currents decay. These clicks are commonly referred to as “click 'n pop” noise.
In large audio equipment, such “click 'n pop” noises are countered by means of relays which isolate the loudspeaker or headset from the amplifier until after power has been supplied to the amplifier. The use of such relays in small audio equipment is undesirable due to the associated additional cost, control complexity and size, and because they cannot be integrated using standard integrated circuit manufacturing processes. The use of transistors to perform an equivalent switching function can cause distortion. There is a requirement for alternative ways of reducing “click 'n pop” noise.